Compression coil springs made of a spiral of material, typically steel, are very commonly used for applications requiring resistance to compressive forces. The life of coil springs is highly variable. They can deteriorate from use, as well as from external factors such as corrosion, or erosion from dust and debris. In some applications, coil springs are constantly being loaded and unloaded, while in other applications the coil springs may remain loaded for long periods of time, including months or years.
For example, one common application for a coil spring is in a magazine for a firearm. A magazine can be fixed within a firearm or removable from the firearm, depending upon the firearm design. A user inserts cartridges into the magazine against the resistance of the spring. If the spring wears out or fails, the firearm may not cycle properly. If a firearm magazine, and thus the spring within it, is continually loaded and unloaded, the spring will weaken, but at least then the user will be able to discern that the spring is weakening because the magazine will become easier to load. In contrast, if a firearm magazine is left loaded for months or years, the user may not realize that the spring has weakened to the point that the operation of the firearm will be compromised. To address this concern, standard law enforcement practice is to rotate magazines every three months. Therefore, there is a need for a spring design that offers better performance, higher reliability, and greater longevity than a coil spring.
One alternative to the coil spring is the Belleville washer, which is also known as a coned-disc spring, conical spring washer, disc spring, or cupped spring washer. A Belleville washer is a washer that is pre-loaded into a frustoconical shape, providing it with the characteristic of a spring. An example of this washer is shown in FIG. 1A. A popular option, shown in profile in FIG. 1B, is for the central hole of the washer to be surrounded by a flat surface known as a contact flat, with the remaining part of the washer having a frustoconical shape. Other shapes are possible. The Belleville washer gets its name from Julien Belleville, who in 1867 patented a spring in the shape of a frustoconical washer.
The Belleville washer, which is preloaded along the axis parallel to its thickness, has a number of advantages. It can support very large loads with a small installation space. Force transmission is absolutely concentric. Varying the height/thickness ratio can produce a wide variety of load deflection curves.
While a single Belleville washer can be used as a spring, and some may use the alternate name Belleville spring to refer to a single Belleville washer, it is also known in the art that a spring can also be formed from a number of the washers that are stacked. In a parallel stack, the stack has the washers oriented in the same direction, so that the convex side of one washer faces the concave side of the adjacent washer, as shown in FIG. 1C. In a series stack, the stack has the washers oriented in an alternate direction, so that the convex side of one washer faces the convex side of the adjacent washer, as shown in FIG. 1D, or so that the concave side of one washer faces the concave side of the adjacent washer, as shown in FIG. 1E. A stack can also include both parallel and series washers, i.e., some washers oriented in the same direction and other washers oriented in alternate directions, as shown in FIG. 1F.
In this application, we will refer to a single disc as a Belleville washer, and will reserve the term Belleville spring to refer specifically to a stacked plurality of the discs.
A stack of Belleville washers can contain a number of identical washers, or can contain Belleville washers that vary in their height, thickness, size, and so forth. When a stack of Belleville washers is properly designed, a large damping effect can be achieved.
The spring rate, also known as spring constant (k), is the constant amount of force or spring rate of force it takes an extension or compression spring to travel an inch of distance or, in the metric system of measurement, a millimeter of distance. In a coil spring, the compressed preload tension (pL) is the compression distance (T) times the spring constant (k), also known as spring rate, which yields a very high spring tension curve. When coil springs combined in parallel, the effective spring constant of the combination is the sum of the individual spring constants. The results in a softer joint, requiring a lesser force to achieve a given amount of deflection. When coil springs are combined in series, the inverse of the effective spring constant of the combination is the sum of the inverses of the individual spring constants. This creates a stiffer joint, requiring a greater force to achieve a given amount of deflection.
How Belleville washers are stacked similarly modifies the spring constant of the stack. Stacking Belleville washers in the same direction is equivalent to combining coil springs in parallel: the effective spring constant of the combination is the sum of the individual spring constants. This creates a stiffer joint, requiring a greater force to achieve a given amount of deflection. Stacking Belleville washers in alternate directions is equivalent to combining coil springs in series: the inverse of the effective spring constant of the combination is the sum of the inverses of the individual spring constants. The results in a softer joint, requiring a lesser force to achieve a given amount of deflection. Mixing and matching directions allow a specific spring constant and deflection capacity to be designed.
Generally, if n Belleville washers are stacked in parallel (facing the same direction), the deflection of the whole stack is equal to that of one Belleville washer divided by n, then, to obtain the same deflection of a single Belleville washer the load to apply has to be n times that of a single Belleville washer. On the other hand, if n Belleville washers are stacked in series (facing in alternating directions), the deflection is equal to n times that of one Belleville washers while the load to apply at the whole stack to obtain the same deflection of one Belleville washer can be that of a single Belleville washer divided by n.
There are many other applications in which a coil spring can be replaced by one or more Belleville washers. In the prior art, Belleville washers are provided with a central hole through which a bolt is passed, as shown in FIG. 1A. The bolt maintains the Belleville washer or washers in position. When a number of Belleville washers are combined in series, in parallel, or in a combination of series and parallel, the bolt maintains the Belleville washers in alignment with each other.
What is required is a Belleville washer that can be combined in series with Belleville washers of identical or similar design, while retaining their alignment, without recourse to using a bolt. In this invention, a Belleville washer uses interlocking teeth to allow one washer to firmly lock to an adjacent washer, allowing for assembly of a modular-type stackable spring.
In a preferred embodiment, the Belleville washer deviates from the traditional frustoconical shape, and instead is shaped as an elliptic paraboloid or the frustum of a pyramid with a curved rectangular base.
Each Belleville disc of the invention can vary in size, cross section, thickness, and material so as to build a configurable type spring collection that varies whatever tensions and shapes are required. In a preferred embodiment, a Belleville spring assembled from a plurality of the Belleville washers of this invention is used in lieu of a compression coil spring, for example in firearm magazines.